Movement discoordination following stroke is caused by the emergence of stereotypic multi-joint movement patterns (synergies), reflecting a loss of independent joint control, and hyperactivity of spinal reflexes, including the stretch reflex (spasticity). Specifically in the paretic upper limb, shoulder abduction/elbow flexion (flexor-synergy) and shoulder adduction/elbow extension (extensor-synergy) are coupled in moderately to severely impaired stroke survivors. As part of the first cycle of this R01 proposal, we quantified these coupling patterns isometrically by using a 6 Degree of Freedom (DOF) load cell. Furthermore, we discovered that subjects are constrained to these abnormal coupling patterns. The general aim of this R01 renewal is to extend the research of discoordination following stroke to arm movement and to elucidate the relative effect of abnormal synergies and spasticity on the 3-D workspace of the paretic limb using 3D robotics. More specifically we intend to: 1) identify and quantify, under dynamic conditions, the effect of gravity on 3-D upper extremity workspace in general and, more specifically, on active elbow/shoulder range of motion;2) determine the relationship between abnormal shoulder/elbow torque patterns and hyperexcitable stretch reflexes during 3-D multi-joint ballistic reaching movements;3) estimate the possible contribution of bulbospinal systems in the expression of abnormal torque patterns and hyperexcitable stretch reflexes using asymmetric tonic neck reflexes (ATNRs) and transcranial magnetic stimulation (TMS) in chronic hemiparetic stroke subjects. We predict that the workspace of the paretic arm will decrease for increasing levels of abduction torques and shoulder abduction angles. This will be studied by changing the level of the subject's arm support and movement direction over horizontal versus inclined and declined planes generated by a 3-D force controlled robot arm. Furthermore, we predict and will provide preliminary evidence that stretch reflex excitability, tested by robot generated stretches at the onset of reaching movements, will increase for increasing level of active limb support. However, since reaching movement will also slow down, we will determine if and when spasticity plays a role in the workspace of the paretic limb. Finally, we predict that the ATNR has a profound effect on the paretic limb's workspace. This expected finding, combined with increased latencies of TMS induced motor evoked potentials (MEPs) and ATNR induced changes in MEP magnitudes in the impaired arm, points to an increased reliance on bulbospinal systems as an important source for discoordination following stroke. Determining the mechanisms underlying upper extremity movement disorders following hemiparetic stroke by using 3D robotics is likely to result in the design of novel therapeutic interventions. These interventions will incorporate 3D robotics-mediated virtual mechanical and visual environments to improve arm function.